The present invention relates to a method of controlling equipment for monitoring the quality of digital television signals.
Equipment for measuring quality, or more precisely for evaluating any possible degradation in quality, is already known and is designed to perform spot measurements, but does not make it easy to perform measurements at different points within a broadcast network, e.g. at the inlet to the network and at various nodes of the network, while also ensuring that the measurements are performed on the same image sequences.
An object of the present invention is to provide a method of controlling monitoring equipment that is capable of providing a solution to that problem.
The invention is based on the idea of generating a digital clock signal which is sampled on each video synchronization signal so as to make it possible to give the measurement equipment a reference for the beginning of the measurements to be performed, and also to time stamp information serving to mark the image sequence(s) to be subjected to measurement.
The invention thus provides a method of controlling equipment for monitoring the quality of digital television signals comprising a data stream organized into frames, the method being characterized in that it comprises the following steps:
a) selecting a reference time signal in the data stream;
b) on the basis of the reference time signal, generating a multibit digital clock signal whose phase is servo-controlled from said reference time signal and whose count is deduced unambiguously from the count of a time base generated during initial encoding of the digital television signals; and
c) transmitting at least meaningful bits of the digital clock signal to the measurement equipment synchronously with an analog video frame synchronizing signal as decoded from the data stream so as to generate a measurement triggering signal. The bits retained are at least those which are meaningful for the kind of measurements performed.
Step a) advantageously includes the following sub-steps:
a1) selecting the frames which correspond to video data associated with a program; and
a2) selecting said reference time signal from said frames.
For example, the digital television signals are in the MPEG-2 standard and during step a1), frames are selected on the basis of the PID field.
Preferably, the specific video data is that on which audio and/or video quality measurements are performed. In which case, the method may include a step of decoding the video data from the frames selected on the basis of said PID field.
The selection of the reference time signal may be performed by testing a flag indicating the presence of said reference time signal in each frame under consideration.
For digital television signals in the MPEG-2 standard, the reference time signal can be the signal PCR or the signal SCR. Advantageously, during step b), said digital clock signal is at a frequency of kxc3x9727 MHz, where k is a non-zero integer or fraction.
The invention also provides equipment for measuring the quality of digital television signals comprising a data stream organized in frames, the equipment comprising:
an identifier device receiving the data stream as input and outputting a reference time signal selected from said data stream;
a clock generator whose phase is lock-ed on the basis of said reference time signal and outputting a multibit clock signal operating at a given frequency and whose count is deduced unambiguously from the count of a time base generated during the initial encoding of the digital video signals;
a sampler receiving on a first input at least meaningful bits of said multibit clock signal and on a second input an analog video frame synchronizing signal present at the output from a data stream decoder, and outputting on each occurrence of said analog video frame synchronizing signal a signal representing the updated value at least of the meaningful bits of the multibit clock signal; and
a measurement device receiving as input said updated value signal and generating as a consequence a signal for triggering measurements.